This invention relates to the field of door security systems. More specifically, this invention relates to the use of exit or panic bars for the emergency egress through a doorway.
Exit bars which allow egress through a doorway during normal and emergency situations are well known in the art of door security systems. Conventional exit bars typically employ a mechanical movement to operate a latch mechanism. This mechanical movement which triggers unlocking of a door results from a force exerted on the exit bar by a person attempting to egress through the doorway. With the increasing use of electromagnetic locks or electrically actuated mechanical locks, exit bars for such locks are responsive to a contact force on the exit bar to actuate an electrical switch which causes the lock to release. Mechanical exit bars, whether directly operating latches or actuating switches to operate electrical locks, typically have the same problems. A mechanical exit bar is subject to wear of the components and to the possibility of becoming jammed. An exit bar jammed in a permanent unlocked state is a risk to security by allowing unauthorized entrance from the outside. An exit bar jammed in a permanent locked state can have catastrophic safety consequences.
As a response to some of the deficiencies of mechanical exit bars, bars which are sensitive to capacitance changes for controlling the operation of electromagnetic locks have been employed. Capacitance sensitive bars, however, can fail if the sensitivity of the electronics is improperly adjusted or changes during operation. In addition, insufficient capacitance change may not be a reliable indicator of a person wanting to egress under all circumstances, for example, when the bar is contacted by an insulated material such as a glove or a coat.